Oxygen consumption in the isolated toad retina

Abstract

Retinal 02 utilization was studied to identify the 02 consuming processes in the retina and the spatial distribution of those processes. Neural retina, retinal pigment epithelium and choroid were dissected from the toad eye and superfused with an oxygenated Ringer's solution. Double-barreled microelectrodes were used to measure 02 and local voltage simultaneously within the retina in both light and dark adaptation. The profile of PO 2 was measured during a withdrawal of the electrode tip across the retinal pigment epithelium and through the neural retina. The PO 2 decreased through the distal retina, reaching a minimum in the inner segment or outer nuclear layer, and then increased steadily through the proximal retina. From fitting PO 2 profiles measured in the dark-adapted retina to a three-layer diffusion model, 02 consumption was found to be 1"0+0"4 and 0'4+0-3 ml 02 (100 g min) -x in the outer and inner halves of the retina, respectively. Light decreased consumption in both halves of the retina. In steady illumination (500 nm) that saturated the ERG b-and c-waves, 02 utilization decreased significantly to 48 % and 68 % of the dark values in the outer and inner retina, respectively. When Na ÷ was removed from the superfusate to inhibit the photoreceptor Na+/K ÷ pump, 02 consumption in the outer retina decreased by about the same amount as in light, but Oz consumption in the inner retina was not significantly affected.

Retinal oxygen: from animals to humans

“…The models just described are the basis for other O 2 models used to derive physiological parameters (Cringle et al, 1996; Cringle and Yu, 2002, 2004; Cringle et al, 2002; Haugh-Scheidt et al, 1995b). They can also be used for predictive simulations, as described in later sections.…”

Calcium regulation in photoreceptors

“…The metabolic and transcriptional activities of photoreceptors are vastly different in light and in darkness (74)(75). Light-dependent integration of metabolism and signaling occurs via second messengers such as Ca 2+ and NO.…”

“…In the retina, production of adenosine is elevated in darkness, possibly as a result of the dramatic turnover of ATP in the IS (74,109). Adenosine is released by depolarized photoreceptors (109) and may be taken up into photoreceptors by adenosine transporters.…”

Intracellular pH modulates inner segment calcium homeostasis in vertebrate photoreceptors

“…Intracellular acidity is often measured in terms of pH i [the negative logarithm, base 10, of the molar concentration of dissolved protons or hydronium ions (H 3 O ϩ )]; a decrease in pH i thus indicates an increase in intracellular H ϩ concentration ([H ϩ ] i ). Intracellular pH (pH i ) and intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) shifts are not independent of each other: while pH i modulates the affinity of intracellular Ca 2ϩ -binding sensor proteins and activity of most known Ca 2ϩ channels and transporters (5, 19 -20, 30, 32-33, 36, 61, 70 -72), changes in [Ca 2ϩ ] i and calmodulin (CaM) activity cause pH i shifts through modulation of Ca 2ϩ /H ϩ and/or Na ϩ /H ϩ exchange mechanisms (44,51,61,67,72).Activity-dependent pH i and [Ca 2ϩ ] i changes are especially pronounced in metabolically active cells, such as vertebrate photoreceptors (26,29,38,59,80). Light and darkness are associated with intracellular production and export of protons (11,21,26,(37)(38).…”

“…Activity-dependent pH i and [Ca 2ϩ ] i changes are especially pronounced in metabolically active cells, such as vertebrate photoreceptors (26,29,38,59,80). Light and darkness are associated with intracellular production and export of protons (11,21,26,(37)(38).…”